What are the power, current, and voltage ratings on the LEDs? (If they have it on the packaging.)
I was going to try to figure out what flasher you would need for the LEDs. But they make a "Variable Load Turnsignal" relay. It is supposed to work under a wide range of loads.
Variable Load Turn Signal Flasher Unit | HelmetHead Cycle Gear™ Motorcycle Accessories Grote Industries: Product #44010 - 3-Wire
While looking for examples online, I found where one guy got one from an auto parts store and it worked perfect. (That seems like what most recomend to do.)
If you don't mind spending more money you can try one of these:
Buy Now: Signal Dynamics Tri Star, Penta Star Module, Turn Signal Modules | Pashnit Moto